The present invention relates to a method and apparatus for advanced wastewater treatment utilizing both bioactivated charcoal and bioactivated carbon.
Hitherto, at wastewater treatment apparatuses of various industrial facilities and research laboratories, it has been general practice to utilize activated carbon for wastewater treatment at a final stage of such treatment, that is, at the stage of advanced treatment. One known way of utilization of activated carbon at the finishing stage or advanced treatment stage of a process for wastewater treatment is simply to take advantage of adsorptive function or physical treatment effect of activated carbon as in a conventional arrangement illustrated in FIG. 5.
On the other hand, there is also known a physico-biological way of utilization such that microorganisms are grown on activated carbon so that physical adsorption function of activated carbon itself and biological treatment by microorganisms grown on the activated carbon can be both utilized.
First, the way of utilization of activated carbon in the conventional wastewater treatment apparatus shown in FIG. 5 is explained. In this wastewater treatment apparatus, two activated carbon towers 101, 102 are filled with activated carbon, and only one of the two towers is supplied with water; but when the quality of the water treated in the one tower becomes lower than a target water quality, water supply is switched over to the other tower. The activated carbon in that activated carbon tower which requires regeneration of its activated carbon content is subjected to regeneration at a separate location. In this conventional apparatus, water feeding and regeneration are alternately carried out in the activated carbon towers 101, 102 in this way. Into the activated carbon towers 101, 102 is introduced treated water after its passage through a pretreatment section 103 and a water quality adjuster pit 105, as shown in FIG. 5. The activated carbon towers 101 and 102 include activated carbon layers 106 and 107 respectively. Treated water from the activated carbon towers 101, 102 is introduced into a treated water tank 108. The COD(Chemical Oxygen Demand) value of treated water in the treated water tank 108 is measured by a COD meter 110. Numeral 111 designates a back washing water tank, numeral 112 designates a back washing pump, and numeral 113 designates a backwash piping.
A wastewater treatment apparatus in which the physico-biological way of activated carbon utilization is used is called a bioactivated carbon treatment apparatus. This apparatus utilizes the adsorptive function of activated carbon relative to substances to be treated and the action of microorganisms grown on activated carbon for decomposition of the adsorbed substances. Examples of such bioactivated carbon treatment apparatus are described in Japanese Patent Application Laid-Open Publication No. 2-229595, and in Japanese Patent Application Laid-Open Publication No. 4-260497.
FIG. 6 schematically shows a bioactivated carbon treatment apparatus by way of example. The apparatus includes a bioactivated charcoal tower 201 having charcoal and the like arranged therein in three dimensions. The bioactivated charcoal tower 201 utilizes charcoal 202 to highly treat organic matter in wastewater. The bioactivated charcoal tower 201 comprises an upper portion or sprinkling circulation section 203 and a lower portion or contact circulation section 205, which are both cubically filled with pieces of charcoal 202. In the tower 201, biofilms are caused to be formed by microorganisms on the charcoal pieces 202, and the water under treatment is circulated upward and downward directions so as to be microbially treated while in circulation.
In the practice of wastewater treatment at various industrial facilities, and semiconductor and liquid crystal plants, a recent trend is that high concentration toxic wastewater containing persistent surfactant which is discharged from them is treated by their own wastewater treating facility. High concentration toxic wastewater, for example, developer liquor containing wastewater discharged from existing semiconductor plants or liquid crystal plants contains tetramethylammonium hydroxide (hereinafter, referred to as TMAH) on the order of 2000 ppm to 10000 ppm. Developer liquor containing wastewater contains, in addition to TMAH, various types of persistent surfactants, alcohols, and colored resists. Specific examples of persistent surfactants contained in developer liquors are alkyl ammonium family surfactant and polyoxyethylene family surfactant.
At such facilities or plants, according to the quality of wastewater, various wastewater treatment techniques are employed including chemical treatment methods, such as neutralization, reaction and coagulation, biological treatment methods, such as biofilm, contact oxidation, activated sludge and special microbial treatment, and physical treatment methods, such as precipitation, filtration, adsorption, floatation and membrane treatment. Treatment stages using these chemical, biological and physical treatment techniques are, hereinafter generically referred to as pretreatment stage.
In reality, these different treatment methods are employed alone or in combination for treatment of high concentration toxic wastewater before the wastewater is discharged (see Japanese Patent Application Laid-Open Publications Nos. 1-9500 and 64-43306). Where stringent effluent standard regulations are in force, conventional wastewater treatment apparatus includes an activated carbon tower or a bioactivated carbon tower at a final operating stage. In this way, where wastewater treatment is carried out within company's own facility, wastewater is subjected to chemical treatment, biological treatment, and/or physical treatment over a long period of time, and the so treated water is finally treated in activated carbon tower or bioactivated carbon tower. In this manner, high-concentration, surfactant-containing toxic wastewater is treated to a quality level lower than statutory control value, the so treated water being then discharged.
Activated carbon placed in such activated carbon tower is rather expensive and involves high running cost because of its short service life prior to regeneration. Recently, therefore, a bioactivated carbon tower of the type earlier described, wherein organic matter is adsorbed by activated carbon on which microorganisms grow so that the microorganisms treat the adsorbed organic matter, is gaining popularity for use. With such bioactivated carbon tower, however, the trouble is that more than one cycle/day of backwash operation is required. Such known tower units, whether they are of the type incorporating activated carbon or of the type incorporating bioactivated carbon, are merely such that activated carbon granules only are placed therein, though various ideas are incorporated with respect to such tower arrangement.
When the construction of wastewater treatment equipment for such an industrial plant as earlier mentioned is undertaken in a local district having good natural environment, with attention directed toward the protection of the local environment, it is not satisfactory that care is simply used to strict observation of legal control values and local regulation values, for there may be some possibility that plant effluent may deleteriously affect the local environment. Therefore, it is necessary that any possible load exerted by such effluent upon the environment be economically reduced as much as possible. In other words, needs exist for a high-efficiency method and apparatus for wastewater treatment which will not cause any unfavorable change to the local environment, is safe in the interest of the local environment, is adapted for advanced wastewater treatment, provides for good cost economy and ease of maintenance, and requires less space for installation.
Meanwhile, conventional techniques for treatment of developer liquor-containing wastewater are simply intended to treat such wastewater so as to meet legal requirements with respect to TMAH(Tetramethyl Ammonium Hydroxide), surface active agents, alcohols, and resist. Therefore, even after wastewater treatment is carried out, trace amounts of persistent surface active agents and resist remain unremoved in treated water. Considerable time is required for decomposition of persistent surfactant. Therefore, if a trace amount of surfactant remains in treated water, it may be a cause of slight foaming of the treated water. A slight amount of resist is likely to color the waste water yellow. For treatment of developer liquor-containing waste water, no attention has been conventionally paid for development of a compact and economical arrangement for preventing such slight foaming and coloring of treated water.
As such, in such a conventional way of treatment as shown in FIG. 5, wherein treatment is carried out by physical adsorption in an activated carbon tower, regeneration of activated carbon is required, and therefore two or more activated carbon towers are required. Further, a backwash water tank, a backwash pump, backwash piping, and the like are required. This involves higher initial cost.
In a conventional bioactivated carbon tower, the water under treatment is subjected to a certain degree of advanced treatment. However, if advanced treatment is carried out only in the bioactivated carbon tower, clogging due to suspended matter is liable to occur, and this necessitates more than one time of backwashing operation every day. Water treatment cannot be carried out during backwashing operation, and this results in decreased volume of treated water. Also, backwashing requires adequate supply of water for the purpose. Further, as a matter of course, a backwash arrangement is required, which leads to higher initial cost. From the standpoint of treated water quality, with one tower alone, any satisfactory quality of treated water cannot be obtained when the water to be treated contains, in particular, persistent surfactants and coloring components, for the treatment of which sufficient time is required. In such a case, with one tower only, any sufficient water quality cannot be obtained, resulting in foaming occurrences. For purposes of treating high concentration wastewater, if a bioactivated carbon tower is provided at a final treatment stage, regeneration of the activated carbon is necessary. Therefore, provision of two or more bioactivated towers is required, resulting in higher initial cost.
In such a method for wastewater treatment using a bioactivated charcoal tower as illustrated in FIG. 6, there is no problem in respect of treatment capability, but it is necessary to arrange that contact reaction time be made longer or the size of the treatment apparatus be made larger because the absorptive capability of the charcoal is not so high.